FIG. 1 is a block diagram of a network structure of UMTS (universal mobile telecommunications system) of 3GPP asynchronous IMT-2000 system.
Referring to FIG. 1, a universal mobile telecommunications system (hereinafter abbreviated UMTS) mainly includes a user equipment (hereinafter abbreviated UE), a UMTS terrestrial radio access network (hereinafter abbreviated UTRAN) and a core network (hereinafter abbreviated CN).
The UTRAN includes at least one radio network sub-system (hereinafter abbreviated RNS). And, the RNS includes one radio network controller (hereinafter abbreviated RNC) and at least one base station (hereinafter called Node B) managed by the RNC. And, at least one or more cells exist in one Node B.
FIG. 2 is an architectural diagram of a radio interface protocol between UE (user equipment) and UTRAN (UMTS terrestrial radio access network) based on 3GPP radio access network specifications.
Referring to FIG. 2, a radio interface protocol vertically includes a physical layer, a data link layer, and a network layer and horizontally includes a user plane for data information transfer and a control plane for signaling transfer.
The protocol layers in FIG. 2 can be classified into L1 (first layer), L2 (second layer), and L3 (third layer) based on three lower layers of the open system interconnection (OSI) standard model widely known in the communications systems.
The respective layers in FIG. 2 are explained as follows.
First of all, the physical layer (hereinafter named PHY) as the first layer offers an information transfer service to an upper layer using a physical channel. The physical layer PHY is connected to a medium access control (hereinafter abbreviated MAC) layer above the physical layer PHY via a transport channel. And, data are transferred between the medium access control layer MAC and the physical layer PHY via the transport channel. Moreover, data are transferred between different physical layers, and more particularly, between one physical layer of a transmitting side and the other physical layer of a receiving side via the physical channel.
The medium access control (hereinafter abbreviated MAC) layer of the second layer offers a service to a radio link control layer above the MAC layer via a logical channel. The radio link control (hereinafter abbreviated RLC) layer of the second layer supports reliable data transfer and is operative in segmentation and concatenation of RLC service data units sent down from an upper layer. Hereinafter, the service data unit will be abbreviated SDU.
A broadcast/multicast control (hereinafter abbreviated ‘BMC’) layer schedules a cell broadcast message (hereinafter abbreviated ‘CB message’) delivered from a core network and plays a role in broadcasting the message to UEs existing in a specific cell(s). In aspect of UTRAN, a CB message delivered from a higher layer is additionally provided with information such as a message ID, a serial number, a coding scheme and the like, is delivered to an RLC layer in a format of BMC message, and is then delivered to a MAC layer via a logical channel CTCH (common traffic channel). And, the logical channel CTCH is mapped to a transport channel FACH (forward access channel) and a physical channel S-CCPCH (secondary common control physical channel).
A packet data convergence protocol (hereinafter abbreviated PDCP) layer lies above the RLC layer and enables data, which is transferred via such a network protocol as IPv4 or IPv6, to be efficiently transferred on a radio interface having a relatively small bandwidth. For this, the PDCP layer plays a role in reducing unnecessary control information used by a wire network. This function is called header compression, for which header compression scheme of RFC2507 or RFC3095 (robust header compression: ROHC) defined by IETF (Internet Engineering Task Force) can be used. In these schemes, information mandatory for a header part of data is transferred only to reduce data volume to be transferred in a manner of transferring smaller control information.
A radio resource control (hereinafter abbreviated ‘RRC’) layer located on a lowest part of the third layer is defined in the control plane only and is associated with configuration, reconfiguration and release of radio bearers to be in charge of controlling the logical, transport and physical channels (hereinafter, the radio bearer will be abbreviated RB). In this case, the RB means a service offered to the second layer for the data transfer between the UE and the UTRAN. And, the configuration of RB means a process of regulating characteristics of protocol layers and channels necessary for offering a specific service and a process of setting their specific parameters and operational methods, respectively.
The RRC layer plays a role in broadcasting system information on BCCH (broadcast control channel). System information for one cell is broadcast to UE in formats of several system information blocks. Hereinafter, the system information block is abbreviated ‘SIB’. In case that system information is modified, UTRAN transmits BCCH modification information on PCH (paging channel) or FACH (forward access channel) to UE. Hence, the UE is enabled to receive latest system information.
A multimedia broadcast/multicast service (hereinafter abbreviated ‘MBMS’) is explained in detail as follows.
First of all, an MBMS offers a streaming or background service to a plurality of UEs using a downlink dedicated MBMS bearer service. One MBMS includes at least one session, and MBMS data are transmitted to a plurality of the UEs via the MBMS bearer service during an ongoing session only. UE performs an activation job to receive a subscribed service and receives a service activated by the UE only.
UTRAN offers an MBMS bearer service to a UE using a radio bearer. As a type of the radio bearer (RB) used by the UTRAN, there is a point-to-point radio bearer or a point-to-multipoint radio bearer. In this case, the point-to-point radio bearer is a bi-directional radio bearer (RB) and includes a logical channel DTCH (dedicated traffic channel), a transport channel DCH (dedicated channel) and a physical channel DPCH (dedicated physical channel) or a physical channel SCCPCH (secondary common control physical channel).
The point-to-multipoint radio bearer is a unidirectional downlink radio bearer (RB). And, the point-to-multipoint radio bearer, as shown in FIG. 3, includes a logical channel MTCH (MBMS traffic channel), a transport channel FACH (forward access channel) and a physical channel SCCPCH. The logical channel MTCH is configured for each MBMS offered to one cell and is used in transmitting user-plane data of a specific MBMS to a plurality of UEs.
A logical channel MCCH (MBMS control channel), as shown in FIG. 3, is a point-to-multipoint downlink channel and is used in transmitting control information associated with the MBMS. The logical channel MCCH is mapped to the transport channel FACH (forward access channel), while the transport channel FACH is mapped to the physical channel SCCPCH (secondary common control physical channel). And, one MCCH exists in one cell.
Configuration information of MCCH is transmitted via system information block (SIB) of BCCH. In case of MCCH reconfiguration, UE firstly receives BCCH modification information transmitted on FACH or PCH, receives SIB according to this information and then obtains MCCH reconfiguration information included in the received SIB.
The UTRAN offering the MBMS transmits MCCH information to a plurality of UEs via the MCCH channel. The MCCH information includes a notification message associated with the MBMS, i.e., an RRC message associated with the MBMS. For instance, the MCCH information includes a message that notifies MBMS information, a message that notifies point-to-multipoint radio bearer information, access information notifying that RRC connection is requested for specific MBMS and the like.
FIG. 4 is a diagram for explaining a transmission method of MCCH information.
Referring to FIG. 4, MCCH information is periodically transmitted according to a modification period and a repetition period. The MCCH information is divided into critical information and non-critical information. In the critical information and non-critical information, the non-critical information can be freely modified each modification period or each repetition period to be transmitted. Yet, the modification of the critical information can be made each modification period only to be transmitted. Namely, the critical information is repeated one time each repetition period to be transmitted. Yet, the transmission of the modified critical information is possible at a start point of the modification period only.
The MCCH information means a control message associated with MBMS, i.e., an RRC message associated with MBMS. A message of MBMS modified services information (hereinafter abbreviated ‘MSI’), MBMS unmodified services information (hereinafter abbreviated ‘USI’), MBMS point-to-multipoint RB information, access information or the like corresponds to the MCCH information. The access information message corresponds to the non-critical information and the rest of the MCCH information messages correspond to the critical information. In this case, the access information is transmitted once each access period equal to or smaller than the repetition period and a length of the repetition period corresponds to a multiplication of an access period length.
In transmitting theses messages, if the corresponding message carries information of a specific service, UTRAN transmits the corresponding message with MBMS transmission identity. In this case, the MBMS transmission identity includes MBMS session identity and MBMS identity. For instance, in case of transmitting MBMS modified services information message, the corresponding message is transmitted with the MBMS transmission identity and information of a service corresponding to the transmission identity.
UTRAN periodically transmits the physical channel MICH (MBMS notification indicator channel) shown in FIG. 3 to indicate whether MCCH information is updated during modification period. So, UE attempting to receive one specific MBMS only does not receive MCCH or MTCH prior to a beginning of a session of the corresponding service but periodically receives MICH (MBMS notification indicator channel). For reference, an update of MCCH information in this specification means creation, addition, modification or removal of a specific item of MCCH information.
And, UTRAN transmits MSI message together with MICH to indicate whether MCCH information is updated during a modification period. The MSI message carries identity information of all service(s) updated during corresponding modification period in a current cell and operation information requested to UE subscribed to the corresponding service. In this case, MBMS transmission identity is used as the identity information. And, the MBMS transmission identity is configured with MBMS identity indicating a specific service only. Alternatively, the MBMS transmission identity can be configured in a manner of combining MBMS session identity and MBMS identity together. Meanwhile, identity information of service(s) not modified during the modification period among services currently provided in a corresponding cell is carried by USI message. In this case, MBMS transmission identity of the corresponding service is used as identity information.
Once a session of a specific MBMS begins, UTRAN transmits NI (notification indicator), which is an indicator notifying UEs to receive MCCH, to the UEs attempting to receive the specific MBMS via MICH. The UE having received the NI via MICH receives the MCCH during a specific modification period. While receiving MCCH, the UE receives MSI message and then checks whether a specific MBMS to be received by the UE is modified during a corresponding modification period. If the specific MBMS is modified, the UE obtains modified MCCH information. Meanwhile, the UE can recognize a list of all services provided in a current cell during the corresponding modification period by receiving MSI and USI messages transmitted for one modification period.
UE, which attempts to receive a specific MBMS using a point-to-multipoint radio bearer, receives MCCH information including radio bearer information via MCCH and then establishes the point-to-multipoint radio bearer using the received information. Having established the point-to-multipoint radio bearer, the UE keeps receiving physical channel SCCPCH, to which MTCH is mapped, to acquire data of the specific MBMS transmitted via MTCH.
UTRAN can discontinuously transmit MBMS data on MTCH. In this case, the UTRAN, as shown in FIG. 5, periodically transmits a scheduling message to UE via MSCH (MBMS scheduling channel) of SCCPCH carrying MTCH. In this case, the scheduling message indicates a transmission start timing point and a transmission interval of MBMS data to be transmitted during one scheduling period. For this, UTRAN has to inform UE of a transmission period (scheduling period) of scheduling information in advance. An MSCH is mapped to SCCPCH carrying MTCH and can exist for each SCCPCH carrying MTCH at most. In this case, the MSCH carrying the scheduling information for the MTCH is MSCH mapped to the same SCCPCH of the MTCH.
Meanwhile, UE preferentially acquires a scheduling period from UTRAN, receives a scheduling message periodically according to the acquired scheduling period, and then receives SCCPCH carrying MTCH discontinuously and periodically using the received scheduling message. Namely, the UE receives the SCCPCH carrying the MTCH during a time interval for transmitting data but does not receive the SCCPCH carrying the MTCH during a time interval for not transmitting data, using the scheduling message.
In case that at least two neighbor cells transmit MBMS of the same information on MTCH, UE receives SCCPCH carrying the MTCH transmitted from the cells by soft combining or selection combining to raise reception sensitivity. In case of soft combining, transport blocks from the cells should be identical during the same time interval. To facilitate UE to perform soft combining, UTRAN transmits transport blocks for one transport channel only during one TTI. And, the UTRAN provides a point-to-multipoint radio bearer information message of the neighbor cells on MCCH as well as a point-to-multipoint radio bearer information message of a current cell to facilitate the UE to perform selection combining reception.
In order to facilitate UE to select cells for combining reception, UTRAN needs to inform UE of a transmission parameter of a transport or physical channel carrying MBMS transmitted by each cell. As an example of the transmission parameter, transmission power information of the transport or physical channel can be taken. Yet, the transmission parameter is not the information mandatory for the UE but is useful in case of the combining reception of a specific service. Hence, it is necessary to selectively transmit the transmission parameter to UEs in need of the transmission parameter.